A multigenerational effect of parental age on offspring size but not fitness in common duckweed (Lemna minor)

Abstract
:

Classic theories on the evolution of senescence make the simplifying assumption that all
offspring are of equal quality, so that demographic senescence only manifests through
declining rates of survival or fecundity. However, there is now evidence that, in addition to
declining rates of survival and fecundity, many organisms are subject to age-related
declines in the quality of offspring produced (i.e. parental age effects). Recent modelling
approaches allow for the incorporation of parental age effects into classic demographic
analyses, assuming that such effects are limited to a single generation. Does this ‘single generation’ assumption hold? To find out, we conducted a laboratory study with the aquatic
plant Lemna minor, a species for which parental age effects have been demonstrated
previously. We compared the size and fitness of 423 lab-cultured plants (asexually-derived
ramets) representing various birth orders, and ancestral ‘birth-order genealogies’. We
found that offspring size and fitness both declined with increasing ‘immediate’ birth order
(i.e. birth order with respect to the immediate parent), but only offspring size was affected
by ancestral birth order. Thus, the assumption that parental age effects on offspring fitness
are limited to a single generation does in fact hold for L. minor. This result will guide
theorists aiming to refine and generalise modelling approaches that incorporate parental age effects into evolutionary theory on senescence.